The invention relates to a longitudinal dynamics control system in motor vehicles.
In the case of motor vehicles having driver assistance systems, particularly for controlling longitudinal dynamics, by which a predefined velocity or a predefined distance from the vehicle driving ahead has to be kept constant, methods are known by which a drive system and/or a wheel braking system are controlled for reaching a desired vehicle velocity. Increasingly, this control takes place by way of the output of a desired wheel torque (or of a desired cumulative wheel torque or a tractive power). With respect to the technical background concerning a potential conversion (implementation) of a desired wheel torque (or a tractive power demand), which can be emitted, for example, by a driver assistance system as a prompt to a drive system, reference is made to German Patent Document DE 101 17 162 A1. The drive system normally consists of an electronically controlled engine (such as an internal-combustion engine) as well as of a transmission which, as required, can also be electronically controlled. The fraction of the wheel torque (cumulative wheel torque) acting from the drive system is therefore obtained as a result of an engine or internal-combustion engine torque at a certain transmission ratio.
Currently implemented driver assistance systems, such as the ACC—Adaptive Cruise Control—or a cruise control of any type predefine their request to the control device of the internal-combustion engine and/or the control device of an automatic transmission by way of a desired predefinition of the clutch torque. This requires the knowledge of the normal resistances and the actual ratio in the transmission line (actual gear and ratio of the differential of the driven axle). The above-described active chain of the driver assistance system—desired predefinition in the direction of the internal-combustion engine, the conversion of the predefinition by the internal-combustion engine and the reaction of the transmission to this conversion has various effects which lead to the following disadvantages:                Long reaction time of the transmission. Downshifting often takes place only when it is no longer necessary.        Superfluous shifting; that is, in certain situations, a downshifting takes place which would not be necessary because the currently available engine torque is sufficient.        Pendulum shifting; that is, frequent down- and upshifting within a short period of time. These may occur particularly at transitions between the plane and a slope or gradient.        
The above-mentioned effects are uncomfortable to the driver because they are unexpected, since the gear shifting differs from that which is carried out without a driver assistance system.
It is an object of the invention to provide a system for controlling longitudinal dynamics which results in an increase of comfort and control speed.
In the case of the system in motor vehicles for controlling longitudinal dynamics by which, starting from an actual vehicle velocity, a new desired vehicle velocity is to be adjusted, a functional module is provided by which a desired wheel torque course predefined for reaching the desired vehicle velocity is determined, which is predefined at least in a main section proportionally to the reciprocal value of the vehicle velocity (compare tractive power hyperbolas) and which is output to potential regulating systems (such as the drive system and/or the braking system) for the conversion of the desired wheel torque course. As a result, the desired predefinition of control of the longitudinal dynamics is adapted, for example, to a traction-power-controlled drive system, as described, for example, in German Patent Document DE 101 17 162 A1.
Furthermore, the functional module is preferably further developed such that at least the main section of the desired wheel torque course is selected between a maximally possible desired wheel torque course and the wheel torque required for keeping the desired vehicle velocity constant.
The desired wheel torque course may be composed of a starting section, a main section and an end section, the starting and the end section representing transition sections with finite gradients.
The starting point of the desired wheel torque course is the wheel torque required for keeping the actual vehicle velocity constant, preferably while taking into account interfering forces or normal resistances. The end point of the desired wheel torque course is the wheel torque required for keeping the desired vehicle velocity constant, also preferably while taking into account interfering forces or normal resistances.
The invention is based on the following recognitions:
As a result of a repositioning of the interface between the system for controlling longitudinal dynamics (driver assistance system) and the drive system (consisting of an arbitrary motor (for example, an internal-combustion engine, a hydrogen drive, an electric motor, etc.) and, as required, an automatic transmission (or an automated manual transmission) to wheel torques, the drive system can first determine which combination of a gear predefinition and of a clutch torque predefinition best converts the momentary wheel torque predefinition. By means of a tractive-power-controlled or wheel-torque-controlled interface to the drive system, the driver assistance system generated a desired predefinition in the form of a wheel torque or a desired wheel torque course proportionally to the reciprocal value of the vehicle velocity or corresponding to the tractive power hyperbolas known from German Patent Document DE 101 17 162 A1. The functional module according to the invention may, for example, be integrated in an electronic control device assigned to the system for controlling longitudinal dynamics, which communicates, for example, with an engine control device and/or a transmission control device. However, the totality of the functional modules in the control devices mentioned here may also be combined in a single central control device or central computer. In this case, the functional modules communicate with one another.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.